SH7708 datasheet(240/633 Pages) RENESAS

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by the LMTS bit in RTCSR, the OVF bit in RTCSR is set and RFCR is cleared. RFCR is

initialized to H'0000 by a power-on reset. It is not initialized by a manual reset or in standby

mode, but retains its contents.

Note:

The method for writing to RFCR is different from that for general registers to prevent

inadvertent overwriting. Using a word transfer instruction, place B'101001 in the top 6 bits

of the upper byte, and the write data in the remaining bits. For details, see section 10.2.13,

Cautions on Accessing Refresh Control Related Registers.

Bit:

Bit name:

—

Initial value:

R/W:

R/W

Bit:

Bit name:

Initial value:

R/W:

R/W

10.2.13

Cautions on Accessing Refresh Control Related Registers

RFCR, RTCSR, RTCNT, and RTCOR require that a specific code be appended to the data when it

is written to prevent data from being mistakenly overwritten by program overruns or other write

operations (figure 10.5). Perform reads and writes using the following methods:

1. When writing to RFCR, RTCSR, RTCNT, or RTCOR, use only word transfer instructions.

Byte transfer instructions cannot be used. When writing to RTCNT, RTCSR, or RTCOR, place

B'10100101 in the upper byte and the write data in the lower byte. When writing to RFCR,

place B'101001 in the top 6 bits and the write data in the remaining bits, as shown in figure

10.5.

2. When reading from RFCR, RTCSR, RTCNT, or RTCOR, use a 16-bit access. 0 is read from

undefined bits.

RTCSR, RTCNT,

RTCOR

RFCR

Write data

Figure 10.5 Writing to RFCR, RTCSR, RTCNT, and RTCOR

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